In vitro induction of drug resistance in pseudomonas aeruginosa to imipenem vs meropenem

Objective To investigate the in vitro induction of drug resistance in pseudomonas aeruginosa to imipenem and meropenem,and based on the time to successful induction,determine which of the two antimicrobials is more readily to show drug resistance.Methods Pseudomonas aeruginosa isolated from patients(20 strains) and another 20 strains of quality controls,both sensitive to common antibiotics,were incubated with broth and subjected to growth for 7 consecutive passages.The minimal inhibition concentrations(MIC) were determined with broth dilution method.Solution of imipenem or meropenem was prepared based on half MIC and then added into the broth.Drug resistance was assessed days later,and when increased,new MIC was determined for the broth to be exposed to new preparations of half-MIC imipenem or meropenem until complete development of antibiotic resistance.Results It took a mean of 4 days for control pseudomonas aeruginosa strains to develop resistance to imipenem vs a mean of 16 days to meropenem.Pseudomonas aeruginos from patients became resistant to imipenem in a mean of 3 days and to meropenem in a mean of 15 days.Conclusion Quality control strains of pseudomonas aeruginosa and pseudomonas aeruginosa from patients gained resistance to imipenem earlier than they did to meropenem.Imipenem appeared more readily to show resistance compared with meropenem.